Bu kodu deneyin, çalışıyor... 

<html>
<head>
<script
  src="https://code.jquery.com/jquery-3.3.1.min.js"
  integrity="sha256-FgpCb/KJQlLNfOu91ta32o/NMZxltwRo8QtmkMRdAu8="
  crossorigin="anonymous"></script>
</head>
<body>
<select class="target renk">
    <option value="mavi">Mavi</option>    
    <option value="kırmızı">Kırmızı</option>
</select>
<br><br><br><br>
  <select class="target yas">
    <option value="56">56</option>
    <option value="12">12</option>
</select>
<br><br><br><br>
<img class="resim" src="">
<script>
$(".target").change(function() {
  var renk= $(".renk").val();
  var yas= $(".yas").val();
  if(renk === "mavi" && yas === "56"){
$(".resim").attr('src','https://via.placeholder.com/300/0048ff?text=56')
   }
    if(renk === "kırmızı" && yas === "12"){
$(".resim").attr('src','https://via.placeholder.com/300/ff0000?text=12')
    }
    if(renk === "mavi" && yas === "12"){
$(".resim").attr('src','https://via.placeholder.com/300/0048ff?text=12')
   }
    if(renk === "kırmızı" && yas === "56"){
$(".resim").attr('src','https://via.placeholder.com/300/ff0000?text=56')
    }

});
</script>
</body>
</html>